The present invention relates to an improved composition for determining the presence of sulfur dioxide.
The problems of sulfur dioxide contamination in air are well-known as sulfur dioxide can be harmful to both personnel and equipment. While exact agreement on the maximum limit of allowable concentration of sulfur dioxide for humans has not been reached, the usually accepted maximum concentration for prolonged exposure is 10 p.p.m. The presence of sulfur dioxide also can denote an equipment failure, such as a venting lithium battery.
Most currently-used methods for determining sulfur dioxide in air depend on bubbling the sample through a solution and measuring the resulting change in some chemical or physical property of the solution (or in some cases, of the gas). Both the acidic and reducing powers of sulfur dioxide are used, and many methods and modifications are in the literature. Nearly all of them require bulky non-portable apparatus or a well-equipped laboratory.
It is known to measure the concentration of sulfur dioxide in a gas mixture by aspirating a sample of the gas mixture through a solution containing a measured amount of standard iodine solution and a starch indicator until the solution is decolorized (the "Reich test"). This test is relatively simple but it gives only spot information and fails to indicate how the process is functioning between tests. Further, it requires the attention of an operator to carry out the test.
It is also known to determine and record continuously the concentration of sulfur dioxide in a gas mixture by absorbing the sulfur dioxide in a measured quantity of electrolyte of known electrical conductivity, such as an aqueous solution of hydrogen peroxide of known concentration, and measuring the change in electrical conductivity of the solution produced by absorption of the sulfur dioxide.
In U.S. Pat. No. 2,785,959, entitled "Colorimetric Determination of Sulphur Dioxide", which issued Mar. 19, 1957, to Gordon D. Patterson and Melvin G. Mellon, there is described a method of determining the concentration of sulphur dioxide in a fluid medium by means of color-changing gels. The color-changing material is produced by treating a gelable siliceous composition with a vanadate salt. The siliceous composition is preferably silica gel and the vanadate salt is preferably ammonium vanadate.